Deposition of metal borides

ABSTRACT

A method for depositing a metal boride film onto a substrate is disclosed. In particular, the method comprises pulsing a metal halide precursor onto the substrate and pulsing a boron compound precursor onto the substrate. A reaction between the metal halide precursor and the boron compound precursor forms a metal boride film. Specifically, the method discloses forming a tantalum boride (TaB 2 ) or a niobium boride (NbB 2 ) film.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to U.S. Non-Provisional patent application Ser. No. 15/135,333, concurrently filed and entitled “DEPOSITION OF METAL BORIDES” and U.S. Non-Provisional application Ser. No. 15/135,258, concurrently filed and entitled “DEPOSITION OF METAL BORIDES AND SILICIDES,” the disclosures of which are hereby incorporated by reference in their entireties.

FIELD OF INVENTION

The present disclosure generally relates to processes for manufacturing electronic devices. More particularly, the disclosure relates to forming metal borides through atomic layer deposition (ALD). Specifically, the disclosure discloses methods to form niobium and tantalum borides.

BACKGROUND OF THE DISCLOSURE

Metal boride films have been formed using various chemical vapor deposition (CVD) methods. In the CVD methods, gaseous source chemicals are introduced into a reaction space at the same time, resulting in a deposition of a metal film on the substrate. In order to thermally activate some of the gaseous source chemicals, the CVD methods tend to take place at temperatures as high as 1200° C. The high substrate temperatures relative to thermal budgets may be problematic, especially for state-of-the-art semiconductor fabrication processes such as metallization.

In addition, physical vapor deposition (PVD) methods have also been used to deposit metal borides. PVD methods generally deposit along a line-of-sight. However, line-of-sight deposition results in insufficient thin film coverage in certain areas where complex substrate contours are involved. Also, line-of-sight deposition results in low-volatility precursors depositing on the first solid surface encountered, leading to low-conformality coverage.

Atomic layer deposition (ALD) has been used to form metal carbide films. For example, U.S. Pat. No. 7,611,751 to Elers discloses methods for forming a metal carbide film through spatially and temporally separated vapor phase pulses of a metal source chemical, a reducing agent, and a carbon source chemical. Similarly, U.S. Pat. No. 8,841,182 to Chen et al. discloses the formation of titanium carbide films through an ALD process. However, no known ALD solution exists to deposit metal boride films at low temperatures. As a result, a method using ALD to form metal boride films is desired.

Further, a method for forming a metal boride film that attains desired dielectric constants as well as demonstrates reliability is desired.

SUMMARY OF THE DISCLOSURE

In accordance with at least one embodiment of the invention, a method of forming a metal boride is disclosed. The method comprises: providing a substrate for processing in a reaction chamber; performing a metal halide precursor deposition onto the substrate, the performing the metal halide precursor deposition step comprises: pulsing a metal halide precursor onto the substrate; and purging an excess of the metal halide precursor from the reaction chamber; and performing a borane compound precursor deposition onto the substrate, the performing the borane compound precursor deposition step comprises: pulsing a borane compound precursor onto the substrate; and purging an excess of the borane compound precursor from the reaction chamber; wherein the metal halide precursor comprises one of: tantalum pentafluoride (TaF₅), niobium tetrafluoride (NbF₄), or niobium pentafluoride (NbF₅); wherein a reaction between the metal halide precursor and the borane compound precursor forms a metal boride film comprising at least one of: tantalum boride (TaB₂) or niobium boride (NbB₂); wherein the metal halide precursor deposition step is repeated a predetermined number of times; and wherein the borane compound precursor deposition step is repeated a predetermined number of times.

In accordance with at least one embodiment of the invention, a method of forming a metal boride is disclosed. The method comprises: providing a substrate for processing in a reaction chamber; performing a metal halide precursor deposition onto the substrate, the performing the metal halide precursor deposition step comprises: pulsing a metal halide precursor onto the substrate; and purging an excess of the metal halide precursor from the reaction chamber; and performing a borane compound precursor deposition onto the substrate, the performing the borane compound precursor deposition step comprises: pulsing a borane compound precursor onto the substrate; and purging an excess of the borane compound precursor from the reaction chamber; wherein the metal halide precursor comprises one of: tantalum pentafluoride (TaF₅), niobium tetrafluoride (NbF₄), or niobium pentafluoride (NbF₅); wherein a reaction between the metal halide precursor and the borane compound precursor forms a metal boride comprising at least one of: tantalum boride (TaB₂) or niobium boride (NbB₂).

For purposes of summarizing the invention and the advantages achieved over the prior art, certain objects and advantages of the invention have been described herein above. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught or suggested herein without necessarily achieving other objects or advantages as may be taught or suggested herein.

All of these embodiments are intended to be within the scope of the invention herein disclosed. These and other embodiments will become readily apparent to those skilled in the art from the following detailed description of certain embodiments having reference to the attached figures, the invention not being limited to any particular embodiment(s) disclosed.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

These and other features, aspects, and advantages of the invention disclosed herein are described below with reference to the drawings of certain embodiments, which are intended to illustrate and not to limit the invention.

FIG. 1 is a flowchart of a method in accordance with at least one embodiment of the invention.

FIG. 2 is a flowchart of a step in accordance with at least one embodiment of the invention.

FIG. 3 is a flowchart of a step in accordance with at least one embodiment of the invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Although certain embodiments and examples are disclosed below, it will be understood by those in the art that the invention extends beyond the specifically disclosed embodiments and/or uses of the invention and obvious modifications and equivalents thereof. Thus, it is intended that the scope of the invention disclosed should not be limited by the particular disclosed embodiments described below.

Metal borides demonstrate potential use in a myriad of applications due to their characteristics. For example, metal borides have a low work function and low resistivity, which make them ideal for n-metal gate or gate fill applications. Also, the high chemical resistance of metal borides makes them applicable for use in patterning layers and hard masks. Furthermore, the high work function and low resistivity of metal borides provide for applicability in p-metal stack, gate fill, and MIMCAP electrodes (SoC).

FIG. 1 illustrates a method for depositing a metal boride in accordance with at least one embodiment of the invention. The method includes a metal halide pulse/purge step 100 and a borane compound pulse/purge step 200. The steps take place within a reaction chamber of an atomic layer deposition device. Such a device may include an EmerALD® XP ALD process module from ASM International N.V. Within the reaction chamber, a substrate to be processed is placed. The substrate may be made of silicon oxide (SiO₂), silicon (Si), silicon germanium (SiGe), germanium (Ge), gallium arsenide (GaAs), or indium phosphide (InP). The substrate may also have a film of titanium nitride (TiN), titanium oxide (TiO₂), hafnium oxide (HfO₂), or another metallic film.

The metal halide pulse/purge step 100 may be repeated after a previous metal halide pulse/purge step via a pathway 300. Similarly, the borane compound pulse/purge step 200 may be repeated after a previous borane compound pulse/purge step via a pathway 310. In addition, the whole process may be repeated via a pathway 320. Such may be desirable in order to form a metal boride film of a desired thickness. For example, 50 cycles of the metal halide pulse/purge step 100 and 50 cycles of the borane compound pulse/purge step 200 may result in the formation of a metal boride film with a thickness of 200 Angstroms.

It is possible that some decomposition of the borane compounds may occur, for example, if the reaction temperature is selected such way that slight decomposition is possible. In particular embodiments, more than a monolayer of borane compound is adsorbed to surface. In other embodiments, more than a monolayer of borane compound is adsorbed to surface, which is then further reacted with the metal halide to form metal boride. In some embodiments, the metal boride film is formed with ALD type of process. In some embodiments, the borane reaction to surface may not be self-limiting to one monolayer due to borane decomposition. In some embodiments, the sequential process may not be an ALD process, but instead a sequential CVD process, for example. In some embodiments, one or more of the purge step(s) may be omitted and replaced by evacuation or removing step steps without the use of inert gas. In some embodiments, one or more of the purge step(s) may be replaced by flowing small concentration of borane compound precursor with or without inert gas. In some embodiments, the borane reaction or metal halide reaction may not form a layer; instead, what may be formed are isolated locations of material or islands, possibly separate or partially connected, of material comprising boron or metal halide, respectively.

FIG. 2 illustrates steps of the metal halide pulse/purge step 100. The metal halide pulse/purge step comprises a metal halide pulse 110 and an inert gas purge 120. Metal halides that may be used in the metal halide pulse 110 comprise tantalum pentafluoride (TaF₅), niobium tetrafluoride (NbF₄), and niobium pentafluoride (NbF₅). In some embodiments, the metal halide may comprise at least one fluorine ligand and the metal is selected to be tantalum (Ta) or niobium (Nb). In some embodiments, the metal halide may comprise tantalum (Ta) or niobium (Nb) with oxidation state +V. In some embodiments, the metal halide may comprise niobium (Nb) with oxidation state +IV. During the metal halide pulse 110, metal halides may be introduced into the reaction chamber through a showerhead precursor delivery system and be incident on the substrate. The metal halide may interact with active sites on the substrate to form a monolayer film of metal halide.

In order to get optimal film formation, there may be optimal settings to run the process. For example, the metal halide may be kept at a temperature of 80° C. prior to entering into the reaction chamber. The temperature within the reaction chamber during the metal halide pulse 110 may range between 200-400° C., which may prove to be beneficial as providing a low thermal budget. In addition, the pressure within the reaction chamber during the metal halide pulse 110 may be between 0.5 to 8 Torr. Each metal halide pulse 110 may take 0.1 to 10 seconds.

The inert gas purge 120 serves the purpose of removing any excess metal halide precursor introduced into the reaction chamber during the metal halide pulse step 110. Inert gases that may be used during the inert gas purge 120 include nitrogen (N₂), argon (Ar), helium (He), hydrogen (H₂), or other rare gases.

FIG. 3 illustrates the borane compound pulse/purge step 200 in accordance with at least one embodiment of the invention. The borane compound pulse/purge step 200 includes a borane compound pulse 210 and an inert gas purge 220.

The borane compound pulse 210 involves a pulsing of a borane compound. Examples of borane compounds that may be used include borane (BH₃), diborane (B₂H₆), triborane (B₃H₈), tetraborane (B₄H₁₀), pentaborane, hexaborane, heptaborane, octaborane, nonaborane, decaborane, and other borane compounds that consist of only boron and hydrogen. Additional borane compounds that may be used include amine boranes, cyclic borides, borazines, borane compounds that do not include carbon, and other boron-containing precursors. When the borane compound pulse 210 commences, the substrate in the reaction chamber may have a monolayer of a metal halide operating as active sites for a borane compound. For example, the substrate may have a layer of niobium pentafluoride when a pulse of diborane is introduced into the reaction chamber. Without disclaiming any theory, it is believed that the diborane reacts with the niobium pentafluoride according to the following equation in order to form a pure niobium boride film: NbF₅+B₂H₆→NbB₂+HF+H₂

Similarly, the reaction of tantalum pentafluoride with diborane would result in the formation of a tantalum boride (TaB₂) film. The formation of pure niobium boride or pure tantalum boride films is advantageous due to properties of oxidation resistance, high chemical resistance, high stiffness and low resistivity in proper phase, for example. Such films have great applicability in, for example, patterning layers, hard masks, back-end-of-line (BEOL) interconnects, gate barriers, and gate fills.

Similar to the metal halide pulse 110, in order to get optimal film formation, there may be optimal settings to run the borane compound pulse 210. For example, the borane compound may be kept at a temperature of 25° C. prior to entering into the reaction chamber. The temperature within the reaction chamber during the borane compound pulse 210 may range between 200-400° C., which allows for a low thermal budget. In addition, the pressure within the reaction chamber during the borane compound pulse 210 may be between 0.5 to 8 Torr. Each borane compound pulse 210 may take between 0.1 to 10 seconds.

The inert gas purge 220 serves the purpose of removing any excess borane compound precursor introduced into the reaction chamber during the borane compound pulse step 210. Inert gases that may be used during the inert gas purge 220 include nitrogen (N₂), argon (Ar), helium (He), hydrogen (H₂), or other rare gases.

As a result of the cycling, a tantalum boride or a niobium boride film may be formed. The film may include a metal-boride bond. On the other hand, the film may include a metal and boron trapped inside the film without a true metal-boride bond. The resulting film may be used in a MOS application, for example. The film may include elements having the following atomic concentrations: (1) Boron from about 30 to about 80%, preferably from about 50 to about 80%, and more preferably from about 60 to about 70%; (2) Metal from about 20 to about 70%, preferably from about 20 to about 50%, and more preferably from about 30 to about 40%; (3) Oxygen having less than about 5%, preferably less than 1%; (4) Hydrogen having less than about 5%, preferably less than 1%; and (5) Fluorine having less than about 5%, preferably less than 1%.

The particular implementations shown and described are illustrative of the invention and its best mode and are not intended to otherwise limit the scope of the aspects and implementations in any way. Indeed, for the sake of brevity, conventional manufacturing, connection, preparation, and other functional aspects of the system may not be described in detail. Furthermore, the connecting lines shown in the various figures are intended to represent exemplary functional relationships and/or physical couplings between the various elements. Many alternative or additional functional relationship or physical connections may be present in the practical system, and/or may be absent in some embodiments.

It is to be understood that the configurations and/or approaches described herein are exemplary in nature, and that these specific embodiments or examples are not to be considered in a limiting sense, because numerous variations are possible. The specific routines or methods described herein may represent one or more of any number of processing strategies. Thus, the various acts illustrated may be performed in the sequence illustrated, in other sequences, or omitted in some cases.

The subject matter of the present disclosure includes all novel and nonobvious combinations and subcombinations of the various processes, systems, and configurations, and other features, functions, acts, and/or properties disclosed herein, as well as any and all equivalents thereof. 

We claim:
 1. A method of forming a metal boride comprising: providing a substrate for processing in a reaction chamber; performing a metal halide precursor deposition onto the substrate, the performing the metal halide precursor deposition step comprises: pulsing a metal halide precursor comprising at least one of niobium tetrafluoride (NbF₄) and niobium pentafluoride (NbF₅) onto the substrate; and purging an excess of the metal halide precursor from the reaction chamber; and performing a borane compound precursor deposition onto the substrate, the performing the borane compound precursor deposition step comprises: pulsing a borane compound precursor onto the substrate; and purging an excess of the borane compound precursor from the reaction chamber; wherein the metal halide precursor comprises a niobium halide; wherein a reaction between the metal halide precursor and the borane compound precursor forms a niobium boride film; wherein the metal halide precursor deposition step is repeated a predetermined number of times; and wherein the borane compound precursor deposition step is repeated a predetermined number of times.
 2. The method of claim 1, wherein the borane compound precursor comprises at least one of: borane (BH₃), diborane (B₂H₆), triborane (B₃H₈), tetraborane (B₄H₁₀), pentaborane, hexaborane, heptaborane, octaborane, nonaborane, decaborane, borane compounds that consist of only boron and hydrogen, amine boranes, cyclic borides, borazines, and borane compounds that do not include carbon, and other boron-containing precursors.
 3. The method of claim 1, wherein a temperature of the reaction chamber ranges between 200 and 400° C.
 4. The method of claim 1, wherein a pressure of the reaction chamber ranges between 0.5 and 8 Torr.
 5. The method of claim 1, wherein the pulsing the metal halide precursor has a duration between 0.1 and 10 seconds.
 6. The method of claim 1, wherein the pulsing the borane compound precursor has a duration between 0.1 and 10 seconds.
 7. The method of claim 1, wherein pulsing a borane compound precursor onto the substrate comprises adsorbing more than one monolayer of the borane compound onto the substrate.
 8. The method of claim 1, wherein one or more of purging the excess of the borane compound precursor and purging an excess of the metal halide precursor comprises flowing the borane compound precursor onto the substrate.
 9. A method of forming a metal boride work function layer comprising: providing a substrate for processing in a reaction chamber; performing a metal halide precursor deposition onto the substrate, the performing the metal halide precursor deposition step comprises: pulsing a metal halide precursor onto the substrate; and purging an excess of the metal halide precursor from the reaction chamber; and performing a borane compound precursor deposition onto the substrate, the performing the borane compound precursor deposition step comprises: pulsing a borane compound precursor onto the substrate; and purging an excess of the borane compound precursor from the reaction chamber; wherein the metal halide precursor comprises one of: tantalum pentafluoride (TaF₅), niobium tetrafluoride (NbF₄), or niobium pentafluoride (NbF₅); and wherein a reaction between the metal halide precursor and the borane compound precursor forms a metal boride comprising at least one of: tantalum boride (TaB₂) or niobium boride (NbB₂).
 10. The method of claim 9, wherein the borane compound precursor comprises at least one of: borane (BH₃), diborane (B₂H₆), triborane (B₃H₈), tetraborane (B₄H₁₀), pentaborane, hexaborane, heptaborane, octaborane, nonaborane, decaborane, borane compounds that consist of only boron and hydrogen, amine boranes, cyclic borides, borazines, and borane compounds that do not include carbon, and other boron-containing precursors.
 11. The method of claim 9, wherein a temperature of the reaction chamber ranges between 200 and 400° C.
 12. The method of claim 9, wherein a pressure of the reaction chamber ranges between 0.5 and 8 Torr.
 13. The method of claim 9, wherein the pulsing the metal halide precursor has a duration ranging between 0.1 and 10 seconds.
 14. The method of claim 9, wherein the pulsing the borane compound precursor has a duration ranging between 0.1 and 10 seconds.
 15. The method of claim 9, wherein pulsing a borane compound precursor onto the substrate comprises adsorbing more than one monolayer of the borane compound onto the substrate.
 16. The method of claim 9, wherein one or more of purging the excess of the boron compound precursor and purging an excess of the metal halide precursor comprises flowing the borane compound precursor onto the substrate.
 17. The method of claim 9, wherein the metal boride has a concentration of Boron from about 30 to about 80 at. %.
 18. The method of claim 9, wherein the metal boride has a concentration of niobium or tantalum from about 20 to about 70 at. %.
 19. The method of claim 9, wherein the metal boride has a concentration of Oxygen of less than 5 at. %.
 20. The method of claim 9, wherein the metal boride has a concentration of Hydrogen of less than 5 at. %.
 21. The method of claim 9, wherein the metal boride has a concentration of Fluorine of less than 5 at. %. 